Integrated circuits (ICs) consist of structured electrically semiconducting, non-conducting and conducting thin layers. These patterned layers are customarily prepared by applying a layer material, for example, by vapor deposition and patterning it by a microlithographic process. By way of the combination of the various electrically semiconducting, non-conducting and conducting layered materials the electronic circuit elements such as transistors, capacitors, resistors and wirings are fabricated.
The quality of an IC and of its function depends particularly on the precision with which the various layer materials can be applied and patterned.
However, with an increasing number of layers the planarity of the layers decreases significantly. This leads to the failure of one or more functional elements of the IC and, therefore, to the failure of the complete IC after a certain number of layers has been reached.
The decrease of the planarity of the layers is caused by the buildup of new layers on top of layers already patterned. By the patterning altitude differences are created which can add up to 0.6 μm per layer. These altitude differences add up from layer to layer and bring about that the next following layer can no longer be applied onto a planar surface but only onto an uneven surface. The first result is that the layer subsequently applied has an irregular thickness. In extreme cases, imperfections, defects in the electronic functional elements and lacking electrical contacts are caused. Moreover, uneven surfaces lead to problems with the patterning. In order to be able to create sufficiently small patterns, an extremely acute depth of focus is a necessary in the microlithographic process step. However, these patterns can only be imaged with acuity on a planar surface. The more the locations deviate from the planarity, the murkier the image becomes.
In order to solve this problem, a so-called chemical mechanical polishing (CMP) is carried out. The CMP causes a global planarization of the patterned surface by the removal of protruding features of the layer until a planar layer is obtained. Because of this, the subsequent buildup can take place on top of a planar surface exhibiting no altitude differences, and the precision of the patterning and of the functionality of the elements of the IC is maintained.
Typical examples for the global planarization are dielectric CMP, nickel phosphide CMP and silicium or polysilicium CMP.
In addition to the global planarization to overcome lithographical difficulties, there are two other important applications for CMP. One is to fabricate microstructures. Typical examples for this application are copper CMP, tungsten CMP or shallow trench isolation (STI) CMP, in particular the Damascene process described below. The other is defect correction or elimination, as for example sapphire CMP.
A CMP process step is carried out with the help of special polishers, polishing pads and polishing agents which are also referred to in the art as polishing slurries or CMP slurries. A CMP slurry is a composition, which in combination with the polishing pad causes the removal of the material to be polished.
In case that wafers with semiconductor layers are to be polished, the precision requirements for the process step and, thus, the requirements set for the CMP slurry are particularly strict.
A series of parameters are used for evaluating the efficiency of CMP slurries and for characterizing their activity. The material removal rate (MRR), that is the speed with which the material to be polished is removed, the selectivity, that is the ratio of the removal rate of the material to be polished to the removal rates of other materials present, the removal uniformity within a wafer (WIWNU; within wafer non-uniformity) and the removal uniformity from wafer to wafer (WTWNU; wafer to wafer non-uniformity) as well as the number of defects per unit of area rank among these parameters.
The copper Damascene process is increasingly used for the fabrication of IC (cf., for example, the European patent application EP 1 306 415 A2, page 2, paragraph [0012]). In order to produce the copper circuit paths, it is necessary to remove a copper layer chemically mechanically in this process with the help of a CMP slurry, which process is also called “copper CMP process” in the art. The completed copper circuit paths are embedded in a dielectric. Customarily, a barrier layer is located between the copper and the dielectric.
The CMP agents or slurries customarily used in these CMP processes contain dispersed, colloidal inorganic particles such as silica particles as abrasive materials.
For example, the US patent application U.S. 2006/0243702 A1 discloses a CMP slurry containing                colloidal silica as an abrasive material,        organic polymeric particles such as polymethyl methacrylate or polystyrene particles which may be integrated with the colloidal silica to form a complex particle,        an oxidizing agent such as hydrogen peroxide,        a water-soluble polymeric compound such as polyvinylpyrrolidone or polyvinyl alcohol,        a first complexing agent forming a water-insoluble complex with copper, having a wet etching rate of less than 3 nm/min and acting as a protective film forming agent, such as quinaldinic acid, quinolinic acid, benzotriazole BTA, benzoimidazole, 7-hydroxy-5-methyl-1,3,4-triazaindolizine, nicotinic acid and picolinic acid,        a second complexing agent forming a water-soluble complex with copper, having a wet etching rate of more than 3 nm/min and acting as a polishing-accelerating agent, such as amino acids, as for example, glycine, alanine or trypophane, or organic acids, such as formic acid, lactic acid, acetic acid, tartaric acid, fumaric acid, glycol acid, phthalic acid, maleic acid, oxalic acid, citric acid, malic acid, malonic acid or glutamic acid or their basic salts with ammonia, ethylene diamine or tetramethyl ammonium hydroxide TMAH, and        surfactants.        
However, there are several disadvantages associated with the use of inorganic particles. Due to their high densities, they have a tendency to settle out of their aqueous dispersions. Consequently, the respective CMP agents or slurries can be unstable. Moreover, these CMP agents fail to adequately control dishing and erosion, corrosion, defects of the surface, polishing rate and selectivity among different materials on the surface. Quite often, the inorganic particles and their aggregates cause scratches in the polished surfaces. However, for obvious reasons, such scratches have to be avoided. Moreover, the various amounts of the first complexing agent and the second complexing agent have to be balanced very carefully: if the amount of the first complexing agent is chosen too high, the MRR is decreased to an undesirable extent (in extreme cases down to 0 nm/min); if the amount of the second complexing agent is chosen to high, the static etch rate SER is increased to an undesirable extent. Both effects leads to a disadvantageous decrease in planarization efficiency.
These problems have been ameliorated to a certain degree by the use of organic particles as the abrasive materials.
For example, the European patent application EP 0 919 602 A1 discloses a CMP slurry comprising                polymeric particles prepared by emulsion polymerization and containing functional groups such as amide groups, hydroxyl groups, methoxy groups or glycidyl groups,        an oxidizing agent, such as hydrogen peroxide, and        a complexing agent forming a water-soluble complex with copper, such as ammonium fluoride, acetylacetone, citric acid, tartaric acid, glycine, catechol, lysine and 2-aminoethanesulfonicacid.        
A similar CMP slurry is disclosed by the European patent application EP 1 036 836 A1, the said CMP slurry containing                polymeric particles prepared by emulsion polymerization and containing hydrophilic functional groups, as for example, polymeric particles consisting of copolymerized methyl methacrylate, methoxypolyethyleneglycol methacrylate, 4-vinylpyridine and containing amino, pyridyl, polyether and ester groups,        colloidal inorganic particles such as fumed silica particles,        an oxidizing agent such as hydrogen peroxide, and        an organic acid such as p-toluenesulfonic acid, dodecylbenzenesulfonic acid, isoprenesulfonic acid, gluconic acid, lactic acid, citric acid, tartaric acid, malic acid, glycolic acid, malonic acid, formic acid, oxalic acid, succinic acid, fumaric acid, maleic acid, phthalic acid, quinaldinic acid, quinolinic acid, nicotinic acid and picolinic acid for improving the polishing rate.        
It is mandatory that the zeta potential of the polymeric particles and the zeta potential of the inorganic particles are of the opposite signs so that both kinds of particles are electrostatically bonded to form composite particles. However, this can cause an undesirable agglomeration of the particles.
Moreover, the European patent EP 1 077 240 B1 discloses a CMP slurry comprising                polymeric particles prepared by radical polymerization of olefinically unsaturated comonomers and containing functional groups such as amino, pyridyl or acrylamide groups that can react with the metal of the surface to be polished,        a complexing agent such as benzotriazole BTA, tolyltriazole, thiourea, benzoimidazole, benzofloxane, 1,2,3-benzothiadiazole, 2-mercaptobenzothiazole, 2-mercaptobenzothiadiazole, 2-mercaptobenzooxazole, melamine, salicylaldoxime, o-phenylenediamine, m-phenylenediamine, catechol and o-aminophenol,        an oxidizing agent such as potassium persulfate, and        a complexing agent acting as a passivating agent selected from the group of complexing agents, in particular, salicylaldoxime, benzotriazole BTA, quinaldinic acid or 7-hydroxy-5-methyl-1,3,4-triazaindolizine.        
However, the problem of staining is not completely resolved by the known CMP slurries. Due to the high density of functional groups such as amino groups or pyridyl groups, the polymeric particles are strongly absorbed on the metal surfaces to be polished, in particular, copper surfaces, which, on the one hand, helps to increase the material removal rate MRR but, on the other hand, leaves the polished surface stained. On the other hand, it frequently happens that no staining occurs but then the MRR can become so low as to be impractical; in extreme cases the MRR is reduced to 0 nm/min. Moreover, as some of the known CMP slurries must also contain inorganic colloidal particles, the danger of scratching is still present.
The problem of scratching can be resolved to a certain degree by a CMP slurry known from the international patent application WO 2005/014753 A1 and comprising                organic polymeric particles consisting of melamine-formaldehyde resins as well as        organic non-polymeric particles consisting of melamine, melamine derivatives such as acetoguanamine, benzoguanamine and dicyandiamide, and their salts as the abrasive materials,        an oxidizing agent,        a chelating agent such as a polyamine like ethylenediamine, 2,2′-bipyridine or diethylenetriamine, a polyaminocarboxylic acid like nitrilotriacetic acid, ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid and their sodium or potassium salts, and an amino acid like glycine, and        a passivating agent like a phosphate, benzotriazole BTA, benzothiazole, 1-H-benzotriazoleacetonitrile, benzotriazole-5-carboxylic acid, 2(3H)-benzothiazolone and 1-H-benzotriazole-1-methanol.        
It is believed that the melamine particles of this prior art CMP slurry are broken up by the shearing forces during CMP at the peaks on the surfaces to be polished. In this way, a high concentration of melamine is generated in situ at these locations, which concentration, in turn, leads to a high material removal rate MRR. However, the static etch SER is also high, whereby the planarization efficiency is decreased. In addition to this, the CMP slurry can still leaves stains on the polished surfaces. Moreover, the effective concentration of the oxidizing agent can be decreased when too high an amount of organic non-polymeric particles is used.